Variable phase shifter, utilizing extensible helical waveguide, for circular te modes



June 21, 1966 c F. DAVIDSON 3,257,630

VARIABLE PHASE SHIFTER, UTILIZING EXTENSIBLE HELICAL WAVEGUIDE, FOR CIRCULAR TE MODES Filed March 50, 1962 NVENTOR CYRIL F. DAVIDSON,

BY M

ATTORNEY United States Patent 3,257,630 VARIABLE PHASE SHIFTER, UTILIZING EXTEN- SiBlLE HELHCAL WAVEGUIDE, FOR CIRCULAR TE MODES Cyril Frank Davidson, Edgware, England, assignor to Her Majestys Postmaster General, London, England Filed Mar. 30, 1962, Ser. No. 183,924 Claims priority, application Great Britain, Apr. 7, 1961, 12,661/ 61 7 Claims. '(Cl. 333-31) This invention relates to electromagnetic waveguides and in particular to a variable phase shifter for use in a circular waveguide propagating the TE mode.

In a waveguide propagating the dominant mode it is fairly easy to produce variable phase change by introducing into the waveguide a slab of high permittivity low loss dielectric suitably tapered at each end to avoid reflections. The dielectric is moved from the region of low electric field intensity near the waveguide wall to the region of high electric field intensity at the centre of the waveguide. Maximum phase change is produced when the dielectric is in the high electric field. It is not possible to adopt a similar technique in circular waveguides propagating the TE mode without producing spurious modes. A phase change can be produced by completelyfilling the waveguide with dielectric, the production of unwanted modes and reflections being minimized by tapering the ends of the dielectric. This method does not, however, enable the amount of phase change produced to be varied unless the waveguide is dismantled and different lengths of dielectric are inserted.

An alternative method of producing a phase change is to vary the length of the transmission path by means of a telescopic joint. With such an arrangement components attached to the waveguide beyond the phase shifter will move but this does not involve serious disadvantage particularly at millimetric wavelengths where the components are usually small. In the case of a telescopic joint however the discontinuity at a joint produces spurious TE modes. Such modes can-be minimized by tapering'the wall of the inner waveguide but they cannot be eliminated completely.

The object of the present invention is to enable a phase change to be effected without the production of spurious modes and according to the invention a variable phase shifter for use in a circular electromagnetic waveguide comprises a closely coiled helix of wire arranged to constitute a portion of the transmission path provided by the waveguide and means for extending or compressing the helix thereby varying the length of said transmission path.

In a particular construction of variable phase shifter embodying the invention, the wire helix has connected at each end a portion of circular waveguide and one of said portions carries a circular cross-section support fixed to one end of a metal sleeve the opposite end of which is slidable on another circular cross-section support provided with an internally threaded ring cap which is in adjustable engagement with a screw thread on the metal sleeve.

One form of waveguide phase changer constructed to operate in accordance with the invention will now be described in greater detail by way of example with reference to the accompanying drawing which is a fragmentary elevation, partly in section of a circular waveguide variable phase changer.

Referring to the drawing, a brass tube 1 has fixed in it at one end a circular cross-section brass end piece 2 to which a circular waveguide section 3A of /8 inch internal diameter is fixed. The other end of the tube has slidable within it another circular cross-section end piece 4 fixed to a circular waveguide section 3B. A knurled 3,257,530 Patented June 21, 1966 ring cap 5 internally screw threaded engages an annular boss or washer 411 on the end piece 4 and is adjustable on an external screw thread on the tube 1. The cap 5 also engages a guide ring 6 on the end of the continuation of the waveguide 3 so that by rotation of the ring the end piece 4 may be moved longitudinally.

The spaced ends of the waveguide are connected together by a closely wound helical spring 7 of 18 standard wire gauge piano wire so that the helix 7 and the waveguide sections 3A and 3B together form a circular waveguide transmission path capable of supporting a TE mode. The helix is 5 inches long and has an internal diameter of inch. The end turns 8 of the helix are screwed into shallow threads cut in the end pieces 2 and 4. In order to maintain the spring 7 straight and in axial alignment with the waveguide sections 3A and 3B, three silver steel guide rods 9 spaced apart at intervals of and of which two only are shown, are arranged to lie in contact with the outside of the spring. The ends 10 of the rods are of reduced diameter and are soldered in the recesses 11 in the end piece 2. The ends 12 of the rods are of reduced diameter and are free -to slide in recesses 13 in the end piece 4.

Rotation of the end cap 5 serves to eliect relative axial movement between the waveguide sections 3A and 3B thereby to compress or extend the helix 7 dependent on the direction of rotation. Thus, the axial length of the transmission path provided by the helix 7 between the waveguide sections 3A and 33 may be varied to change the phase of a wave travelling along the helix. Since the transition to the helical waveguide offers no discontinuity to the TE mode the setting up of spurious modes is avoided.

I claim:

1. A TE mode electromagnetic waveguide variable phase shifter for conducting a TE, mode wave without the introduction of spurious modes, comprising a resilient cylindrical helix of electrically conductive wire having adjacent turns sufficiently close that the helix can support a TE, mode waveguide transmission, first and second mounting members secured one to either end of the said helix, said mounting members defining means for coupling the respective ends of the said helix to circular waveguide means, an electrically conductive sleeve surrounding said helix in closely spaced relation therewith and having one end secured to said first mounting member, and adjustment means cooperable with both the said second mounting member and the said sleeve to effect movement of the second member relatively towards and away from the said first member respectively to compress and extend the said helix and vary the length of the TE waveguide transmission path-defined between the ends of the helix.

2. A TE mode electromagnetic waveguide variable phase shifter for conducting a TE mode wave without the introduction of spurious modes, comprising two circular waveguide sections, a resilient cylindrical helix of electrically conductive wire, first and second mounting members connecting said helix at either end thereof to the said two waveguide sections with adjacent turns of the helix sufliciently close to define a TE mode waveguide transmission path between the two said waveguide sections, an electrically conductive sleeve member surrounding said helix in spaced relation therewith, said sleeve having one end fixedly secured to said first mounting member, and adjustment means cooperable with both the said second mounting member and the said sleeve to effect relative movement of said second member and the waveguide section to which it is connected longitudinally towards and away from the waveguide section connected to said first mounting member respectively to compress and extend said helix and vary the length of the TE waveguide transmission path defined by the said helix between the said two waveguide sections and means for mounting said two waveguide sections and the said helix in axial alignment with each other and arranged to permit the said relative movement between the two said waveguide sections. 7

3. A variable phase shifter as claimed in claim 1, in

which means for maintaining the walls of the said'helix straight are mounted between the said first and. second members. 4. A TE mode electromagnetic waveguide variable phase shifter, comprising two circular waveguide sections, a resilient cylindrical helix of electrically conductive wire, means connecting the helix at either end thereof to the said two waveguide sections with adjacent turns of the helix sufiiciently close to define a TE mode waveguide transmission path between the said two waveguide sections, and means for effecting relative movement of the two waveguide sections longitudinally towards and away from each other whereby respectively to compress and extend the helix thereby to vary the length of the waveguide transmission path defined by the helix between the said two waveguide sections.

5. A TE mode electromagnetic waveguide variable phase shifter, comprising two circular waveguide sections, a resilient cylindrical helix of electrically conductive Wire, first and second members coupling the ends of the said helix to the respective two waveguide sections, adjacent turns of the said helix being sufficiently close that the helix defines together with the two said waveguide sections at TE waveguide transmission path, a cylindrical sleeve extending longitudinally of the said helix in spaced relationship therewith, the said first member fixedly secured to the said sleeve to close one end thereof, the said second member being slidably mounted in the bore of the sleeve at the opposite end thereof, a cap member rotatably mounted on the second member, and threadedly co-operating means on the said cap member and the second member whereby rotation of the cap member effects movement of the first and second members relatively towards or away from each other respectively to compress or extend the said helix thereby to vary the longitudinal length of the TE waveguide transmission path provided by the said helix between the said waveguide sections.

6. A variable phase shifter as claimed in claim 5, and

further comprising a plurality of guide rods extending between the said first and second members and spaced around the circumference of the said helix for maintaining the helix straight and in axial alignment with the said two waveguide sections, the said guide rods permitting the said relative movement between the first and second members to compress and extend the helix.

7. In a circular electromagnetic waveguide defining a TE mode transmission path, a variable phase shifter comprising a cylindrical resilient helix of electrically conductive wire having an internal diameter equal to that of the said circular waveguide, first and second annular cross-section members coupling the said helix in the said circular waveguide, an electrically conductive sleeve surrounding the said helix in spaced relationship therewith, the first member fixedly secured within the bore of the said circular waveguide, first and second annular mounted in the bore of the sleeve at the opposite end thereof and in longitudinal slidable relationship with the sleeve, a ring cap rotatably mounted on the said circular waveguide, threadedly co-operating means on the sleeve and thering cap for effecting relative sliding movement between the sleeve and the second member whereby to move the first and second members longitudinally towards and away from each other respectively to compress and extend the said helix, a plurality of guide rods extending between and supported by the said first and second members to permit the said relative movement between the first and second members, the said guide rods spaced about the periphery of the said helix to maintain the walls thereof straight and the helix in axial alignment with the said circular waveguide, and adjacent turns of the said helix being sufiiciently close that the helix defines part of the TE mode transmission path provided by the said circular waveguide and the said compression and extension of the said helix alters the length of the said part of the transmission path provided by the helix to effect phase changes in an electromagnetic wave propagated along the said waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,848,695 8/ 1958 Pierce 333- 2,848,696 8/1958 Miller 333--95 2,934,671 4/1960 Rich 333-31 2,966,643 12/1960 Kohman 33395 3,108,238 10/1963 McHenry 333-81 HERMAN KARL SAALBACH, Primary Examiner. ELI LIEBERMAN, Examiner. C. BARRAFF, Assistant Examiner. 

1. A TEON MODE ELECTROMAGNETIC WAVEGUIDE VARIABLE PHASE SHIFTER FOR CONDUCTING A TEON MODE WAVE WITHOUT THE INTRODUCTION OF SPURIOUS MODES, COMPRISING A RESILIENT CYLINDRICAL HELIX OF ELECTRICALLY CONDUCTIVE WIRE HAVING ADJACENT TURNS SUFFICIENTLY CLOSE THAT THE HELIX CAN SUPPORT A TEON MODE WAVEGUIDE TRANSMISSION, FIRST AND SECOND MOUNTING MEMBERS SECURED ONE TO EITHER END OF THE SAID HELIX, SAID MOUNTING MEMBERS DEFINING MEANS FOR COUPLING THE RESPECTIVE ENDS OF THE SAID HELIX TO CIRCULAR WAVEGUIDE MEANS, AN ELECTRICALLY CONDUCTIVE SLEEVE SURROUNDING SAID HELIX IN CLOSELY SPACED RELATION THEREWITH AND HAVING ONE END SECURED TO SAID FIRST MOUNTING MEMBER, AND ADJUSTMENT MEANS COOPERABLE WITH BOTH THE SAID SECOND MOUNTING MEMBER AND THE SLEEVE TO EFFECT MOVEMENT OF THE SECOND MEMBER RELATIVELY TOWARDS AND AWAY FROM THE SAID FIRST MEMBER RESPECTIVELY TO COMPRESS AND EXTEND THE SID HELIX AND VARY THE LENGTH OF THE TEON WAVEGUIDE TRANSMISSION PATH DEFINED BETWEEN THE ENDS OF THE HELIX. 